Just a few decades ago, an unexpected death or serious mishap during surgery was viewed as a tragic but unavoidable event by patients and their families, and by the public at large. Lawsuits were rare, and settlements were modest.
Today, the average patient in reasonable health who enters a hospital fully expects clinicians to provide care with a near-zero risk of complication or death. If a procedure leads to loss of life or major impairment, the damage is no longer regarded as acceptable, especially when it is thought to be the result of avoidable technical or human failure. These incidents now lead to major malpractice suits against hospitals and physicians.
One of the most important aspects of critical care is the clinician's management of the patient's airway. Typically, this involves placement of an endotracheal (or airway) tube in the trachea of the patient. Oral intubation of the human trachea has become a routine procedure used to maintain a clear airway in most surgical, emergency, and intensive care situations. Intubations are performed in the hospital and in the field by individuals of differing backgrounds and levels of training. Failure to achieve tracheal intubation, resulting in the airway tube being placed in the esophagus and diverting air flow from the lungs, can cause patient complications (morbidity) or death (mortality) and is a continuing source of clinicians' anxiety.
The problem is acute because there are an estimated 18 million surgeries performed under general anesthesia each year in the United States alone. In addition, one million acute heart attack patients and three million trauma patients are admitted to hospitals each year. Most of these patients require mechanical ventilation and thus require tracheal placement of an airway tube.
In addition, there are other situations, typically in the field, where intubations are performed by paramedics or other individuals with less background and training than is typically found among hospital personnel. Misplacement of airway tubes (unrecognized esophageal intubation) by these individuals also contributes significantly to morbidity and mortality statistics.
A review of various anesthesia-related morbidity and mortality statistics indicates that unrecognized esophageal intubation is a problem, even among those members of the medical population specifically trained in the tracheal intubation technique. An analysis of anesthetic accidents reported to the Medical Defense Union of the United Kingdom from 1970-1978 revealed that nearly half of the cases resulting in death or cerebral damage were due to faulty clinical technique. The procedure most often identified as the source of mishap was tracheal intubation with inadvertent esophageal--rather than tracheal--tube placement.
Another reviewer of anesthesia-related medical liability claims in the United Kingdom from 1977 to 1982 listed esophageal intubation as a "main cause" of accidents leading to death or neurologic damage with the largest monetary claims resulting from such mishaps.
An investigation of anesthesia-related deaths in Australia revealed that 69% of these deaths were related to airway mismanagement with esophageal intubation once again identified as a major contributing factor.
In one institution in the United States, unrecognized esophageal intubation was identified as a significant problem in a study of cardiac arrests that had been attributed solely to anesthesia. There were twenty-seven cardiac arrests among 163,240 anesthetic cases over a fifteen year period. Of these twenty-seven cardiac arrests, four were attributed to esophageal intubation.
In the state of Kansas, five malpractice cases involving improper intubation were settled for one million dollars each in 1984-85. Four new cases alleging improper intubation were brought before Kansas courts in the first six months of 1986; at issue were two deaths and two brain-damage cases, all involving patients who were having elective surgeries.
In reviewing malpractice claims brought against anesthesiologists in Washington State from 1971-1982, researchers found that esophageal intubation figured prominently among complications resulting in cardiac arrest, brain damage, and death. Of 192 claims, seven were brought for unrecognized esophageal intubation.
The foregoing makes it clear that a reliable technique for confirming that tracheal intubation has been achieved would be of signal importance to the medical profession. Techniques providing signs which may, in some circumstances, indicate that a successful tracheal intubation has been accomplished include the following:
Direct Visualization
Direct visualization of the vocal cords and observation as the airway tube passes into the trachea is considered by many the "gold standard" of correct tube placement, and this remains one of the more reliable signs. Unfortunately, direct visualization is impossible to achieve in certain patients, even in the most experienced hands, due to a multitude of factors. Clinicians and medics are thus often called upon to make "blind" intubations in which the position or condition of the patient is such that the progress of the tube cannot be followed visually. For example, it may be dangerous to immediately move an accident victim, or there may be insufficient lighting where a patient has collapsed at home. "Blind" intubations are performed in the hospitals as well, especially in patients who are overweight or have anatomical abnormalities. The problem is more common is inexperienced hands and may be associated with haste, poor lighting, or an individual patient's anatomical abnormality. Often, the clinician's view may be obstructed by the advancing tube, by acute angulation of the airway in the back of the patient's throat, or by a loss of depth perception with monocular vision.
Even if visualization of the vocal cords and tracheal tube placement has been achieved, the tube may be inadvertently withdrawn from the trachea before or during securing of the tube or when moving the patient to the lateral or prone position. Additionally, radiographic studies have shown that flexion or extension of the neck can change tube positions as much as five centimeters, resulting in inadvertent extubation which may well not be observed by the clinician.
Chest Movement
Another commonly relied upon method of confirming tracheal intubation is observation of symmetric bilateral movements of the chest wall during ventilation. Some patients, however, have physical conditions in which ventilation is more than usually dependent on diaphragmatic movement as opposed to chest wall movement. Patients with large breasts, obesity, a barrel chest from lung disease, and other conditions tend to develop rigid chest walls. Chest movement can be difficult to evaluate in these circumstances, making assessment of proper tube position by chest expansion unworkable.
More importantly, movement of the chest wall simulating ventilation of the lungs can be seen even with the ventilating tube positioned in the esophagus. Distension of the stomach with air can cause outward movement, mimicking the downward movement of the diaphragm and outward movement of the lower chest. Escape of gas from the stomach through the esophagus with release of bag compression would allow the diaphragm to fall and would move the lower chest inward, creating the false impression that there is exhalation from the lungs. Confirmation of this phenomenon exists in numerous reports and studies. At least one study demonstrated chest movements "identical to those seen when the lungs were inflated" where, in fact, stomach ventilation had been established through an airway tube intentionally inserted into the esophagus.
Breath Sounds
The presence of bilateral breath sounds from a stethoscope placed over each of the lungs would seem to be a strong reassurance of proper tube position based on experience and common sense. However, the literature documents numerous cases involving experienced clinicians where apparently normal breath sounds were present with esophageal ventilation. Air passing through the esophagus has been noted to resemble coarse or tubular breath sounds, and it has been suggested that the combination of esophageal wall oscillation with gas movement and acoustic filtering can produce wheezes similar to the sounds arising from lungs ventilated mechanically or by hand.
Presence of Exhaled Tidal Volume
This method of confirming tracheal intubation can be uncertain because it is possible to have measurable tidal volumes of air moving in the airway tube during spontaneous respiratory efforts with the esophagus intubated and the trachea obstructed. Researchers have documented tidal volumes of up to 180 milliliters and peak flows of greater than fifty liters per minute under these circumstances.
Reservoir Bag Compliance
Another practice commonly employed is noting the characteristic feel of the reservoir bag associated with normal lung compliance during inspiration and the presence of expiratory refilling of the bag during hand ventilation. However, compliance varies widely from one person to another and within the same individual at different times. Repeated filling and emptying of the stomach with esophageal ventilation, leading to inflation and deflation of the breathing bag, can also be mistaken for pulmonary ventilation.
Airway Tube Cuff Maneuvers
With the cuff deflated, the higher pitched sound of air escaping around a tracheal tube, compared to the more guttural of leakage around an esophageal tube, has been used as a distinguishing feature. However, with the cuff of an esophageal tube located near the level of the cricoid cartilage, the distinction in air sounds may not exist. Also, palpation of the airway tube cuff in the neck to verify position has been reported to fail, perhaps because the easily distensible esophagus simply balloons outward with an inflated cuff inside it.
Air Escape
A less commonly performed procedure involves pressing sharply on the chest while listening over the tub=opening to detect "a characteristic feel and sound of expelled air." This procedure is unreliable because of the inability to distinguish between air expelled from the tracheal tube and: (1) air passing through or around an esophageal tube, or (2) esophageal air present from mask ventilation prior to intubation, or (3) air expelled from the nose.
Tube Condensation
Condensation of water vapor in the tube, although less likely with esophageal intubation, can occur and hence is not a reliable sign. Conversely, the absence of condensation normally seen with a tube positioned in the trachea would be reason to look for further proof of correct tube position.
Pulse Oximetry
Although useful in many situations, pulse oximetry may be an untimely indicator of esophageal intubation for several reasons. Researchers have noted normal functioning of a ventilator when connected to an esophageal tube. With the vocal cords relaxed, patients were studied after deliberate intubation of both the esophagus and trachea. Ventilation into the esophagus also caused some ventilation of the lungs, as evidenced by carbon dioxide recordings obtained from the open tracheal tube. This ventilation could significantly slow the onset of oxygen desaturation of the blood after esophageal intubation and could delay recognition of esophageal tube placement until surgery is in progress. Also, the practice of preoxygenation of patients prior to intubation can slow the recognition of an improper tube position using pulse oximetry because the patients' blood is highly saturated with oxygen at the start of the surgical procedure.
End-Tidal Carbon Dioxide Measurement
End-tidal carbon dioxide measurement offers perhaps the most reliable and simplest determination of proper tube placement. It involves the measurement of carbon dioxide concentration during the respiratory cycle. The reliability of carbon dioxide monitoring is based on the assumption that carbon dioxide can be reliably detected in patients with an intact pulmonary circulation and an intubated trachea whereas no carbon dioxide is present in gases exiting from an esophageal tube. Carbon dioxide can be detected initially with esophageal intubation when carbon dioxide has been forced into the stomach during prior mask ventilation. However, the end-tidal carbon dioxide is low in such cases; the wave pattern is irregular; and the carbon dioxide levels rapidly diminish with repeated ventilation, making it easy to distinguish between carbon dioxide from the trachea and that from the esophagus.
The disadvantage of this test is that it takes a relatively expensive monitoring device. Also, this device is too cumbersome for routine use in all settings where it would be needed; and it must be connected to an electrical power source during the intubation procedure. This is disadvantageous because power may not be available where, or when, intubation is needed.
In short, the position of the airway tube employed to achieve tracheal intubation of a patient and thereby manage his or her airway must be checked on each insertion; and there are a large number of tests available to confirm tracheal placement of the tube. However, considerable evidence challenges the relative merits of these heretofore available tests. Also, there has been, up to now, no single device which can or would be used in all situations to detect misplacement of airway tubes in the esophagus. Furthermore, clinical studies have shown that, even with the detection of seemingly proper signs by experienced clinicians, an airway tube may have been placed in the esophagus. Also, a number of the just-discussed techniques for confirming tracheal intubation employ monitoring devices; and those devices each lack one or more of the following attributes, all of which are either required for the monitoring device to be successful or important in obtaining this goal:
Ease of use
The device must be easy to connect to the airway tube, require no more than minimal interpretation of the indication, and require no electrical power.
Sensitive
The device must display an obvious indication of carbon dioxide expired from the lung within thirty seconds.
Reliable
The indicator must not give false-positive readings but may show transitory readings from a limited volume of carbon dioxide or other materials from the stomach.
Inexpensive
The device should desirably sell for less than $1.00 U.S. in large quantities.
Disposable
To avoid cross-contamination, the device should be designed for single patient use.
Clean
The device should be designed to be cleaned during assembly in accordance with ANSI Code 279.2 for tracheal tube connectors and adapters.
Save
The device must not allow components to which it is attached to become disconnected or otherwise impede the normal ventilation of the patient.
Rugged
The device must withstand severe stresses without disconnecting from its mating tube.
Storable
The device must have a shelf life of twenty-four months prior to use without loss of effectiveness.
From the foregoing, it can be seen that undiagnosed esophageal intubation figures prominently in anesthesia-related morbidity or mortality and related malpractice suits. The commonly utilized methods of assessing tube position are all unsatisfactory under the circumstances encountered in tracheal tube placement. Expired carbon dioxide measurement is currently the most reliable means under all circumstances of determining proper tube position, but this method suffers from the requirement that an expensive monitoring device be attached to the airway tube before correct placement can be verified. Thus, the usefulness of this procedure in emergency conditions is limited; and it is relegated to formal hospital settings. There is no inexpensive product currently available which provides a simple test for carbon dioxide expired by the patient through the airway tube to verify tracheal tube placement.